1. Field of the Invention
The invention relates to a thrust bearing where multiple rolling elements are rollably arranged between an inner ring and an outer ring.
2. Description of the Related Art
In an existing art, for example, a thrust bearing for supporting a thrust load is used as a bearing that supports a main shaft of a crusher mill. The main shaft of the crusher mill rotates with respect to a housing. Such a thrust bearing is, for example, described in Japanese Patent Application Publication No. 2005-282714 (JP-A-2005-282714). The thrust bearing is a roller thrust bearing that is formed of an inner ring (shaft washer), an outer ring (housing washer), a plurality of tapered rollers, and a solid-type retainer. The inner ring is fitted to a rotary shaft. The outer ring is fitted to a housing. The tapered rollers are rollably arranged between the inner ring and the outer ring. The solid-type retainer has pockets for retaining the tapered rollers at predetermined intervals in the circumferential direction.
Because an extremely large thrust load acts on a roller thrust bearing that supports a main shaft of a crusher mill, the roller thrust bearing need to be provided with as many rollers as possible to have a higher loading capacity. Therefore, a pin-type retainer shown in FIG. 3 may be used. The pin-type retainer may be provided with more rollers than the solid-type retainer.
The pin-type retainer 100 includes a pair of inside ring 104 and outside ring 105, and pins 106. The inside ring 104 and the outside ring 105 are arranged at positions on respective sides of each tapered roller 103 in the axial direction of the tapered roller 103 and between an inner ring 101 and outer ring 102 of the roller thrust bearing. The pins 106 pass through through-holes 103a of the tapered rollers 103. Each pin 106 has a threaded shaft 106a at its one end. The threaded shaft 106a is screwed into a threaded hole 105a of the outside ring 105 that is arranged on the outer side of the tapered roller 103 in the axial direction of the tapered roller 103. The other end of each pin 106 is fixed by a weld 107 to an inner peripheral surface 104a of the inside ring 104 that is arranged on the inner side of the tapered roller 103 in the axial direction of the tapered roller 103.
In the pin-type retainer 100 shown in FIG. 3, because the other end of each pin 106 is fixedly welded to the inner peripheral surface 104a of the inside ring 104, the inner peripheral surface 104a may radially deform due to welding distortion, which deteriorates the out-of-roundness thereof. Therefore, as the rotation guide for the pin-type retainer 100, it is not possible to employ a shaft guide where the inner peripheral surface 104a of the inside ring 104 slides on the rotary shaft 108, and there is no other choice but to employ a roller guide where the tapered roller 103 guides the rotation of the pin-type retainer 100. The radial position of the tapered roller 103 is determined by a rib 109 of the outer ring 102. In the roller thrust bearing that supports the main shaft of the crusher mill, the axis of the rotary shaft 108 may largely offset from that of a housing 110 or the rotary shaft 108 may be inclined with respect to the housing 110. As a result, the axis of the inner ring 101 and the axis of the outer ring 102 may largely offset from each other, or a large offset load may be applied. If the axis of the rotary shaft 108 offset from the axis of the housing 110 or the rotary shaft 108 receives an offset load, the rotary shaft 108 may contact the inner peripheral surface 104a of the inside ring 104. If the rotary shaft 108 contacts the inner peripheral surface 104a of the inside ring 104 that is radially deformed due to welding distortion, the pin-type retainer 100 does not smoothly rotate, which causes a problem that the rotation performance of the roller thrust bearing decreases.
When the distance between the rotary shaft 108 and the inner peripheral surface 104a of the inside ring 104 is increased so that the rotary shaft 108 does not contact the inner peripheral surface 104a of the inside ring 104 even if the axis of the rotary shaft 108 largely offsets from the axis of the housing 110, it is necessary to reduce the length of each tapered roller 103. As a result, a loading capacity decreases.